NFL teams will draft more than 220 players this week. Odds are most, if not all of them will be college students.

That’s because NFL teams cannot draft anyone they want. The NFL requires that players “have been out of high school for at least three years and must have used up their college eligibility before the start of the next college football season.” Some college juniors can apply for a waiver from the league to enter the draft a year early, but they’re not the majority.